Previously only now, but now you can have maximum 3 adlink units. Keep in mind you are not obliged to use them all, actually it usually makes sites uglier if you have too many ads.
Yeah, you can use three, but I've found it better to keep your pages simple and just put in one or two ads (I often use an ad block up top with the content wrapped around it and then an AdLinks unit at the bottom of the article where people are looking for something else to click).